A low drop-out voltage regulator is a regulator circuit that provides a well-specified and stable DC voltage (whose input-to-output voltage difference is typically low). The operation of the circuit is based on feeding back an amplified error signal which is used to control output current flow of a pass device (such as a power transistor) driving a load. The drop-out voltage is the value of the input/output differential voltage where regulation is lost.
The low drop-out nature of the regulator makes it appropriate (over other types of regulators such as dc-dc converters and switching regulators) for use in many applications such as automotive, portable, and industrial applications. In the automotive industry, the low drop-out voltage is necessary during cold-crank conditions where an automobile's battery voltage can be below 6V. Increasing demand for LDO voltage regulators is also apparent in mobile battery operated products (such as cellular phones, pagers, camera recorders and laptop computers), where the LDO voltage regulator typically needs to regulate under low voltage conditions with a reduced voltage drop.
A typical, known LDO voltage regulator uses a differential transistor pair, an intermediate stage transistor, and a pass device coupled to a large (external) bypass capacitor. These elements constitute a DC regulation loop which provides voltage regulation.
For the (LDO) low drop-out voltage, generally in the closest known technology the load capacitor forms the dominant pole, and due to this the capacitor has to be specified with a minimum and maximum serial resistance. As the load is part of the regulation loop, it is possible for instability to be caused by such indeterminate factors as parasitic capacitance.
However, this approach has the disadvantage(s) that, since the load is part of the regulation loop:                the LDO regulator typically needs an external capacitor in order to ensure stability.        the loop DC gain changes versus the load resistance and the capacitor value        the capacitor has to be specified with a minimum and maximum ESR (Equivalent Serial resistor)        
A need therefore exists for a low drop-out voltage regulator in wherein the abovementioned disadvantage(s) may be alleviated.